Optical control device and optical control method

ABSTRACT

An optical control system receives an incident light wave containing a plurality of wavelength components and is capable of giving different spatial light intensity distributions respectively to the wavelength components and of easily changing the color characteristic of an outgoing light wave. The optical control system is applied to illumination systems and light sources for displays, and to a method and an apparatus for process control using such modulated light. The optical control system receives a linearly polarized light wave as an incident light wave  1  containing a plurality of wavelength components, gives different polarization plane rotation angles respectively to the wavelength components by a wavelength dispersion azimuth rotator  3,  gives the plane of polarization of the incident light wave  1  an optional optical rotation angle spatial distribution by a spatial light modulator  5,  and emit an outgoing light wave containing wavelength components respectively having different spatial light intensity distributions by an analyzer  7.

TECHNICAL FIELD

The present invention relates to a new spatial light modulating systemcapable of giving different spatial light intensities respectively tothe component waves of incident light and of readily changing the colorcharacteristic of outgoing light, to the application of the spatiallight modulating system to illumination systems and light sources fordisplays, and to a method and an apparatus for process control usingsuch modulated light.

BACKGROUND ART

Techniques for changing the color characteristic of light emitted by alight source can be applied not only to illumination systems and lightsources for displays but also to many uses including laser machining,laser plasma x-ray generation and laser fluorescent microscopes. It isexpected that a method capable of providing many kinds of colorcharacteristics in a wide spectral range can be applied to a widevariety of industrial fields. Known techniques provide light waves ofdifferent color characteristics by using a plurality of light sourcesrespectively capable of emitting light waves of different colorcharacteristics, changing the respective intensities of the light wavesindividually and mixing the intensity-modified light waves or by passingwhite light wave through a plurality of different color filters.

The method of providing light waves of different color characteristicsby using a plurality of light sources, individually modulating theintensities of light waves and mixing the intensity-modulated lightwaves needs a complicated apparatus. The method using the color filtershas difficulty in changing many kinds of color characteristics. Thus ahighly flexible method capable of simply changing the colorcharacteristic of a light wave emitted by a light source for one of manykinds of color characteristics has been desired.

A simple method has been desired to provide a spatial distribution oflight waves of desired different wavelengths through the optical pulseshaping of a laser beam consisting of light waves of differentwavelengths.

A coherent laser beam can be focused in a diameter on the order of itswavelength by an optical condenser system. The coherent laser beamhaving such a characteristic and capable of propagating at an ultrahighpropagation speed equal to the light velocity of 300,000 km/s is appliedto controlling various precision high-speed processes. In laser plasmax-ray generating processes and laser machining processes, the intensityof x-rays, machining efficiency or accuracy are dependent on manyparameters including the wavelength, spatial intensity distribution andwaveform of the laser beam.

For example, the temperature and density of a plasma produced by a laserplasma x-ray generation process vary in a complicated mode with time andin space in a short time. Therefore, light capable of accuratelycontrolling the temperature of the plasma according to the spatial andtemporal development of the laser plasma must be used for irradiation togenerate x-rays of a specific wavelength efficiently and to keep thelaser plasma at an optimum temperature.

Particularly, when a pulse laser that emits laser pulses of a narrowpulse width is used, a plasma of a ultrahigh temperature is generatedwhen condensed high-intensity laser pulses of a narrow pulse width isapplied to a target in a vacuum and a plasma region of micrometersexpands at a high speed in the range of several tens to several hundredskilometers per second. Therefore, a control method effective in a veryshort time range is needed.

Therefore, the light for controlling the plasma is required to achieveaccurate control to keep the electron temperature of the plasmaspatially and temporally at an optimum temperature in, for example,laser plasma x-ray generation and to make a reaction process approach anoptimum path.

The reaction process can be made to approach an optimum path bycontrolling temporal pulse waveform and spatial light intensitydistribution. However, it has been difficult to control spatial lightintensity distribution and temporal pulse waveform simultaneously.Particularly, in a region of control where the response speed limit ofliquid crystal is on the order of microseconds, the simultaneous controlof the spatial light intensity distribution and temporal laser beamwaveform needs a large, complicated apparatus and is very difficult.

For example, a method of shaping pulses of laser light having aplurality of wave components of different wavelengths uses a tunablelaser and spatial light modulator in combination. The tunable laser makea laser medium having a wide optical amplification wavelength bandoscillate at a specific wavelength selected by a wavelength selectingfilter, such as a diffraction grating or a prism. A diffraction gratinghaving an acoustooptic device can be made to perform high-speed responsewavelength light pulse oscillation by electrically controlling thediffraction grating.

When a laser beam emitted by a tunable laser is divided into componentlaser beams by wavelength by a dichroic mirror or the like, thecomponent laser beams are passed through spatial light modulatorsrespectively having different modulation patterns for specificwavelengths and the modulated component laser beams are mixed, differentspatial light intensity distribution can be given to light pulses ofdifferent wavelengths.

Wavelength changing speed is dependent on the wavelength changing speedon the order of microseconds at the highest of the optical wavelengthfilter or on the wavelength changing speed on the order of millisecondsof the spatial light modulator. Therefore, the changing speed of thespatial light intensity distribution determined by the combination ofthose elements cannot be shorter than milliseconds as a factor of ratecontrol.

A method of modulating phases of the wavelength components of a veryshort light pulse is mentioned in Reference 1. This method applies avery-short light pulse to one of two paired diffraction gratings,separates the light pulse by wavelength on the basis of the diffractionangle dispersion characteristic of the diffraction grating, collimatesthe wavelength components dispersed by diffraction angle by a lens sothat the optical axes are parallel inserts a liquid crystal spatiallight modulator in a Fourier plane formed by spectral development in adirection perpendicular to the optical axis, focuses the wavelengthcomponents passed through the light modulator by a lens on the otherdiffraction grating for optical synthesis to produce an outgoing lightpulse having an adjusted relative phase as temporal positions forwavelength.

The temporal pulse waveform can be optionally changed in an ultrashorttime by an acoustooptic adjustable dispersion filter (AOPDF). Accordingto this paper, experiments compressed an ultrashort light pulse of 30 fsto provide an ultrashort light pulse of 17 fs.

Those methods give the same spatial light intensity distributionpatterns for all the wavelength components. Thus those methods have alow degree of freedom of optical adjustment and cannot give differentlight intensity distribution patterns to the wavelength components.

A temporal pulse waveform shaping method of the Mach-Zehnderinterferometry system is mentioned in Patent document 1. This temporalpulse waveform shaping method divides a short laser light pulse into aprimary pulse and a secondary pulse by a beam splitter, delays theprimary or the secondary pulse by an optical delay circuit to provide atwo-pulse laser beam and irradiates a metal target with the two-pulselaser beam to generate x-rays. This temporal pulse waveform shapingmethod is able to adjust the interval between the pulses and therespective optical intensities of the primary and the secondary pulseindividually. However, nothing about using pulses different from eachother in wavelength is disclosed and mentioned in Patent document 1.

A pulse generating method mentioned in Reference 3 generateshigh-intensity laser light pulses of femtoseconds having a polarizationstate subject to change with time. This pulse generating method dividesan incoming laser light pulse generated by a chirp pulse amplificationmethod into a reference light wave and a signal light wave by a beamsplitter. The reference light wave is polarized into a 45° linearlypolarized light wave having an x- and a y-component by a half-wave plateto fix the delay time of the reference light wave relative to the signallight wave. The signal light wave is made to fall on an interferometerto generate a time-dependent polarized light pulse. The time-dependentpolarized light pulse is combined coaxially with the reference lightwave at relative delay time by a beam splitter and are divided into anx- and a y-component by a polarizer (polarization beam splitter). Aspectroscope receives the x- and the y-component and generates aspectral interference signal of the x- and the y-component. Thus a pulsehaving a time-dependent polarization characteristic can be generated bydividing the high-intensity laser light pulse of femtoseconds by aninterferometer to delay one of the components of the polarized lightrelative to the other, and multiplexing the components of differentphases again.

This method, however, cannot adjust the spatial light intensitydistribution and hence cannot provide a laser beam that enablesprocessing of a high degree of freedom using wavelengths of differentlight intensities.

A light pulse control method previously proposed by the inventors of thepresent invention in Jpn. Pat. App. No. 2002-073365 divides ashort-pulse laser beam into two laser beams by a half mirror, developsan optical path difference between the two laser beams by an opticaldelay circuit, and adjusts spatial light intensity distributions of thelaser beams on the optical paths by a deformable mirror.

A series of sheet-form light pulses provided with a plurality of kindsof spatial light intensity distributions must be prepared andirradiation must be performed at proper time intervals in a short timeto control the temperature of a temporally and spatially developinglaser plasma so that a reaction process approaches an optimum path togenerate x-rays of a specific wavelength. Therefore, an opticalapparatus built by combining a plurality of optical systems like anoptical system disclosed in Jpn. Pat. App. No. 2002-073365 is needed.However, such an optical system is large and complicated.

An alignment-free optical demultiplexer mentioned in Patent document 2does not have any mechanical drivers and employs a Faraday rotator, a TN(twisted nematic) liquid crystal and an analyzer. This opticaldemultiplexer produces a polarization direction difference of 90°between two linearly polarized light waves which are used for opticalcommunication, namely, a linearly polarized light wave of 1.3 μm inwavelength and a linearly polarized light wave if 15 μm in wavelengthand separates the linearly polarized light waves by the analyzer. Thisinvention does not have any technical idea of increasing the degree offreedom of optical control by adjusting spatial light intensitydistribution simply by changing the two wavelength components.

An optical isolator mentioned in Patent document 3 employs a Faradayrotator, a TN liquid crystal and an analyzer. This optical isolator hasan optically active liquid crystal rotator and a Faraday rotator placedbetween a polarizer that transmits a specific linearly polarized lightwave and an analyzer. The Faraday rotator rotates a polarization planein the same direction regardless of the direction of travel of the lightwave. Therefore, when the Faraday rotator is adjusted so as to transmita forward light wave, the polarizing plate intercepts a backward lightwave. This optical isolator is a device for passing and stopping opticalcommunication signals and does not have any idea of adjusting spatiallight intensity distribution.

None of the light modulators based on the prior art derives variouscolor characteristics from a light source and gives desired spatiallight intensity distributions for a plurality of different wavelengthcomponents. There has not been any means for giving different spatiallight intensity distributions for wavelength components at a timedifference of milliseconds. To achieve the ideally precise control of aprocess, it is preferable to set optimum spatial light intensitydistributions for wavelength components by using a light wave consistingof a plurality of wavelength components and to set phase differencesoptionally for wavelength components.

Active studies have been made in recent years for the measurement andcontrol of chemical processes using ultrashort light pulses. Studies arebeing made at present for the quantum control of chemical reactionprocesses and the control of laser plasma x-ray ultrahigh-speedprocesses using ultrashort light pulses. It is apparent that furtheraccurate process control can be achieved if both the light pulsestructures of a temporal region and a spatial region can besimultaneously controlled.

When it is desired to control a temporal characteristic and a spatialcharacteristic simultaneously, as regards an ultrashort light pulsetemporal region, the response speed of the known method using thespatial light modulator employing the liquid crystal or the known methodusing the deformable mirror is not sufficiently high. Therefore, aconventionally used method combines pulse strings respectively havingdifferent spatial light intensity distributions by a system including anoptical delay circuit and a spatial light intensity distribution controloptical system in combination.

A representative one of such optical system was applied to an ultrahighresolution fluorescent microscope of an STED system (stimulated emissiondepletion system) reported by S. W. Hell of Finland in 1994. Theapplication of the optical system to the ultrahigh resolutionfluorescent microscope of an STED system is a special example which issatisfactory when two light waves have intensity distributions. To makethe application of the optical system to a wide variety of usespossible, many kinds of light intensity distributions need to bedeveloped on a time axis. Thus, problems in the dimensions, efficiencyand costs of the optical system make the practical application of theoptical system impossible.

Patent document 1: JP 08-213292 A

Patent document 2: JP 10-161064 A

Patent document 3: JP 05-214400 A

Reference 1: Kaminari Fumihiko, et al., “Femtosecond Laser Pulse Shapingby Adaptive Control and Application to Optical Pumping”, Reiza Kenkyu,pp. 479-485, August, 2000

Reference 2: F. Verluise, et al., “Amplitude and Phase Control ofUltrashort Pulses by Use of an acousto-optic Programmable DispersiveFilter: Pulse compression and Shaping:, OPTICS LETTERS, Vol. 25, No. 8,pp. 575-577, Apr. 15, 2000, Optical Society of America

Reference 3: Kakehata Masanosuke, “Generation of High-intensityFemtosecond Laser Pulses Having Polarization State Changing with Time”,Reiza Gakkai Gijutsu Koen-kai, 22nd Nenji Taikai Koen Yokou-shyu, pp.13-14, January, 2002

DISCLOSURE OF THE INVENTION

It is a first object of the present invention to provide a simpleoptical apparatus and a method capable of easily producing light wavesof a plurality of color characteristics by continuously changing thecolor characteristic of a light wave emitted by a light source in a widerange.

A second object of the present invention is to provide a laser pulsecontrol method capable of simultaneously and precisely adjusting spatialintensity distributions and temporal waveforms for wavelength componentsof laser light in a range of time intervals of a millisecond or belowexceeding the limit of response speed of optical switching of aferroelectric liquid crystal, and a simple optical apparatus forcarrying out the laser pulse control method.

A third object of the present invention is to provide an opticalapparatus provided with an adjusting mechanism for adjusting laser lightto achieve precisely process control, such as the selective control ofthe intensity of x-rays of a specific wavelength when various materialsor specimens are irradiated with a laser beam to generate laser plasmax-rays, and an optical control method to be carried out by the opticalapparatus.

A fourth object of the present invention to provide an apparatusprovided with a simple optical system capable of generating fluorescenceexciting light and fluorescence suppressing light for anultrahigh-resolution scanning laser fluorescence microscope of a STEDsystem, and an optical control method.

An optical control system in a first aspect of the present inventionincludes: an optical rotatory device having an optical rotatorydispersion characteristic that changes optical rotation angle accordingto wavelength; an analyzer; and a spatial light modulator capable ofchanging the optical rotation angle of the polarization plane of anincident light wave by the entire region of an entrance surface or byparts of the entrance surface; wherein the optical rotatory device, thespatial light modulator and the analyzer are arranged so that theincident light wave passes the azimuth rotator, the spatial lightmodulator and the analyzer in that order.

The optical control system of the present invention receives a linearlypolarized light wave including wavelength components, passes thelinearly polarized light wave through the optical rotatory device todivide linearly polarized light wave into the wavelength componentsrespectively having different optical rotation angles, makes lightpassed through the optical rotatory device fall on the spatial lightmodulator with the entire entrance surface or with parts of the entrancesurface adjusted to an optical rotatory power corresponding to theoptical rotation angle of one of the wavelength components, adjusts theoptical rotation angles of the polarization planes of the wavelengthcomponents so as to be in a predetermined relation with the direction ofthe analyzer, and passes the light wave through the analyzer to emit anoutgoing light wave including wavelength components respectively havingspatial light intensities.

The optical rotatory device having an optical rotatory dispersioncharacteristic that changes optical rotation angle according towavelength is an optical rotatory device made of a natural opticalrotatory material containing an optically active substance, such as aquartz crystal or a TN liquid crystal or a Faraday rotator.

A quartz crystal and a TN liquid crystal have optical rotatory poweronly in a specific direction. When the traveling direction of a lightwave is reversed, the rotating direction of the polarization plane isreversed. Therefore, when a light wave passed through the foregoingsubstance in one direction passes the substrate in the oppositedirection, the polarization plane of the light wave coincides with theinitial polarization plane. While the optical rotatory power of thequartz crystal is scarcely subject to the influence of an electric fieldand a magnetic field, the optical rotatory power of the TN liquidcrystal changes according to the field strength of an electric fieldapplied to the TN liquid crystal. An isotropic substance, such as ascroll solution, exerts optical rotatory power on a light wave travelingtherethrough in an optional direction.

The faraday rotator uses the Faraday effect, i.e., the rotation of theplane of vibration of light when the light passes through a substance.According to the Faraday effect, the rotation angle of the plane ofvibration is proportional to the product of the strength H of themagnetic field, the length L of a pass of light in a substance and thecosine of angle φ between the direction of propagation of light and themagnetic field when the substance is nonmagnetic. The proportionalconstant V is called Verdet's constant. The proportional constant V isdependent on the quality of the substance and wavelength. When thesubstance is magnetic, the angle of Faraday rotation is not proportionalto the magnetic field but proportional to magnetization.

The Faraday rotator is characterized in that the direction of rotationof the polarization plane does not change when the traveling directionof light is reversed. The optical isolator mentioned in Patent document3 utilizes this characteristic that does not change the direction ofrotation of the polarization plane when the traveling direction of lightis changed.

The optical rotatory dispersion characteristic of most Faraday rotatorsis stronger than that of rotators using a natural optically activesubstance. The optical rotatory device using a bismuth-iron garnetcrystal (Bi₃Fe₅ crystal), in particular, has high optical rotatorypower. When a light wave of a wavelength in the range of 700 to 800 nmis passed through a bismuth-iron garnet crystal in the state ofsaturation magnetization in the direction of a magnetic field, apolarization plane rotation deviation of about 18,000° per onecentimeter of the length of the propagation path of the light wave isproduced. Therefore, if the crystal has a thickness of 50 μm, a magneticrotatory dispersion for the wavelength is on the order of 90°.

When an incident light wave is passed first through a polarizer, thelight wave becomes a light wave having a predetermined polarizationplane even if the incident light wave is not a linearly polarized lightwave. Therefore, the light wave can be processed similarly to a linearlypolarized light wave as mentioned in connection with the description ofthe optical control system of the present invention.

A TN liquid crystal is a representative example of the spatial lightmodulator included in this optical control system that changes thepolarization angle of the incident light wave by rotation. The TN liquidcrystal exercises a twisted nematic effect.

The TN liquid crystal is a TN cell formed by sandwiching an about 10 μmthick layer of a nematic liquid crystal of a positive dielectricanisotropy between two glass substrates provided with transparentelectrodes so that the major axes of liquid crystal molecules aretwisted continuously through an angle of 90° between the two substrates.The pitch of twist of the TN cells is sufficiently long as compared withthe wavelength of visible light. Therefore, the direction ofpolarization of an incident linearly polarized light wave fallenperpendicularly to the substrates rotates through 90° according to thetwist of the liquid crystal molecules as the linearly polarized lightwave travels through the layer of the TN liquid crystal. Thus theincident light wave is rotated through 90°. When a voltage is applied tothe TN cell, the major axes of the liquid crystal molecules startturning in the direction of an electric field as the voltage increasesbeyond a threshold voltage Vth. The TN cell saturates at a voltage abouttwice the threshold voltage Vth. Since the optical rotation angle of theincident linearly polarized light wave is dependent on the twist of theliquid crystal molecules, the optical rotation angle approaches 0° asthe voltage increases. Thus the optical rotation angle of the incidentlinearly polarized light wave can be adjusted by adjusting the voltageapplied to the liquid crystal cell.

Minute cells, to which adjusting voltages are applied individually, of aliquid crystal device can be formed in a close arrangement by formingtransparent electrodes by a circuit printing technique. Therefore, zonesdefined by properly dividing a surface on which the incident linearlypolarized light wave falls can determine proper optical rotation anglesfor polarization planes, respectively.

When a light wave containing wavelength components respectively havingdifferent polarization plane rotation angles falls on this liquidcrystal device, the polarization plane rotation angles determined by thezones of the entrance surface are added to the polarization planerotation angles of the wavelength components respectively havingdifferent wavelengths. Consequently, a wavelength component having atotal polarization angle coinciding with the direction of a transmissionpolarization plane emerges as an outgoing light wave from the opticalcontrol system.

Thus a part of the entrance surface of the liquid crystal devicedetermines the outgoing wavelength component and the TN liquid crystaldevice functions as a spatial light modulator. The inclination of thepolarization plane of a light wave passed through the spatial lightmodulator does not coincide with the direction of a transmissionpolarization plane of the analyzer, the quantity of light that passesthe analyzer varies according to the difference between the inclinationof the polarization plane of a light wave passed through the spatiallight modulator and the direction of the transmission polarization planeof the analyzer. Thus the intensities of wavelength components of alight wave can be adjusted.

The optical control system in the first aspect of the present inventionpasses the incident linearly polarized light wave having a plurality ofwavelength components through the optical rotator having opticalrotatory dispersion, changes the polarization angles for wavelengthcomponents, and passes the light wave through the spatial lightmodulator having the polarization plane rotator having a single zone ora plurality of individual zones to adjust spatial light intensitydistributions to predetermined patterns for the wavelength components.

The ability to determine spatial light intensity distributions for thewavelength components corresponds to an ability to determined spatialdistributions for color characteristics. Therefore, various variationsof the foregoing methods of illumination and displaying are possible.

The optical control system of the present invention combined with anoptical device capable of controlling phases of wavelength components,namely, a wavelength phase modulator, is capable of adjusting thetemporal light pulse waveform to a predetermined pattern simultaneouslywith the adjustment of spatial light intensity distribution patterns topredetermined patterns for wavelength components.

A light pulse shaping optical system called a Fourier light synthesisoptical system is an example of the wavelength phase modulator. TheFourier light synthesis optical system includes a diffraction grating,an optical focusing system, a spatial light modulator, an opticalfocusing system and a diffraction grating arranged in that order atintervals corresponding to the focal distance of the optical focusingsystem. The diffraction grating decomposes an incident light waveincluding a plurality of wavelength components by spectraldecomposition, the optical focusing system performs spectral developmentin a direction perpendicular to the optical axis, the spatial lightmodulator changes the optical path lengths of the wavelength componentsto adjust phase differences to predetermined values. The light wavepassed through the diffraction grating, the optical focusing system andthe spatial light modulator is passed through the optical focusingsystem and is converged in a light beam by the diffraction grating. Thusthe Fourier light synthesis optical system provides a light beamcontaining the wavelength components developed on the time axis.

The spatial light intensity distributions of the wavelength componentsof the light wave can be precisely adjusted and the temporal waveformcan be adjusted by using the wavelength phase modulator in combinationwith the optical rotator or the spatial light modulator. The opticalcontrol system of the present invention can be easily built byassembling a plurality of optical devices. The temporal and spatialconstruction of light, namely, the spatial light intensity distributionand temporal waveform, can be easily and accurately controlled by theoptical control system of the present invention.

An optical control system in a second aspect of the present inventionincludes: an optical rotatory device; and a spatial optical phasemodulator capable of changing the phase of incident light by the entireregion of an entrance surface or by parts of the entrance surface;wherein the incident light passes the optical rotatory device and thespatial optical phase modulator in that order.

The spatial optical phase modulator modulates the phase of only apolarized light wave polarized in a direction parallel to one of twoperpendicularly intersecting coordinate axes perpendicular to itsoptical axis. The spatial optical phase modulator can be formed by usinga nematic liquid crystal having liquid crystal molecules with theirmolecular axes oriented in the same direction.

A linearly polarized light wave having a plurality of wavelengthcomponents is passed through the optical rotatory device to make thewavelength components have specific optical rotation angles,respectively, and the light wave passed through the optical rotatorydevice is made to fall on the spatial optical phase modulator having anentrance surface having parts respectively having adjusted phasechanges. Since the wavelength components have polarization planes ofdifferent inclinations, respectively, the wavelength components havedifferent ratios between components polarized in directions parallel totwo perpendicularly intersecting coordinate axes, and an outgoing lightwave is a synthesized light wave of a wavelength component processed byspatial optical phase modulation and a wavelength component notprocessed by spatial optical phase modulation. When the outgoing lightwave is focused by a focusing optical system, a far field pattern ofwavelength components having different spatial light intensitydistributions is formed.

The spatial optical phase modulator produces different phase delays bychanging the optical path length of only a polarized component in adirection parallel to one of two coordinate axes defining a planeperpendicular to the optical axis of a light wave. The spatial opticalphase modulator can employ a two-dimensional optical phase modulatorusing the anisotropic refractive index of a nematic liquid crystal.

The two-dimensional optical phase modulator is a liquid crystal devicethat controls only phase without entailing the rotation of apolarization plane by arranging liquid crystal molecules having ananisotropic refractive index with their major axes aligned with adirection perpendicular to the optical axis. When a voltage is appliedacross transparent electrodes spaced by a liquid crystal layer, themajor axes of the liquid crystal molecules are inclined to the opticalaxis at an angle proportional to the voltage applied across thetransparent electrodes and thereby phase delay of the light wavepolarized in the direction of the major axes is changed. The phase ofthe wavelength components polarized in a direction perpendicular to thedirection of the major axes of the liquid crystal molecules does notchange even if the direction of the major axes is changed by the voltageapplied across the transparent electrodes. The ratio between a polarizedwavelength component parallel to the major axes of the molecules and apolarized wavelength component perpendicular to the major axes of themolecules of an incident linearly polarized light wave is dependent onthe direction of polarization. Therefore, the phase delay is dependenton the polarization angle of the incident light wave. Phase delay isdependent also on the applied voltage.

Proper voltages are applied to two-dimensional positions on the spatialoptical phase modulator, and a linearly polarized light wave having aplurality of wavelength components is passed through the azimuthrotator. Consequently, the polarization planes of the wavelengthcomponents of the incident linearly polarized light wave are rotatedthrough different angles and the linearly polarized light wave falls onthe spatial optical phase modulator on which a two-dimensional phasedelay pattern is formed. An outgoing light wave emerging from thespatial optical phase modulator is a synthesized light wave includingpolarized wavelength components processed by spatial optical modulationaccording to different polarization angles for wavelengths correspondingto different voltages applied to positions on the entrance surface ofthe spatial optical phase modulator and polarized wavelength componentsnot processed by spatial optical phase modulation in different ratios.

The wavelength components and the orthogonal polarized light componentsof a near field intensity distribution, namely, a near field pattern,formed on the exit surface of the spatial optical phase modulator and alight wave having a near field phase distribution interfere with eachother in the focusing optical system and form a far field pattern havingdifferent light intensities for wavelength components and correspondingto the near field pattern at the focal point of the focusing opticalsystem. Therefore, the spatial optical phase modulator is adjusted so asto produce a near field phase distribution suitable for forming anecessary far field pattern. A method of forming a far field patternfrom a near field pattern and a near field phase distribution isestablished by wave optics and the far field pattern can be previouslyknown through simulation and experiments.

Thus the spatial light intensity of the far field pattern can becontrolled without passing the outgoing light wave through the analyzerwhen the spatial optical phase modulator is used and hence light energycan be efficiently used without attenuating the light wave.

If a polarizer is disposed above the optical rotor with respect to thedirection of travel of a light wave, the polarization plane of a lightwave incident on the optical rotatory device can be selectivelydetermined and hence the same effect can be expected even if a lightwave other than a linearly polarized light wave is used.

A process, such as a thermal reaction process for melting orevaporations, a nuclear reaction process, a plasma reaction process, achemical reaction process, an isotope separation process or afluorescent light emission process, can be caused by irradiating amatter with laser pulses having a plurality of wavelength components andproduced by the temporal and spatial control of the temporal and spatialconstruction of light pulses. These processes are applied to the controlof laser machining, synthesis, decomposition and separation of chemicalsubstances and elements, production of atoms, molecules, ions,electrons, positrons, neutrons and clusters of particles, generation ofelectromagnetic radiations, such as x-rays and y-rays, and emission offluorescent light. Application of the foregoing techniques toindustries, such as the semiconductor industry, the chemical industry,the energy industry, the medical industry and the machine industry,particle accelerators and basic studies, such as examination ofbiological substances, is expected.

The characteristic of x-rays can be precisely controlled through theadjustment of the spatial intensity distribution and temporal waveformof a laser beam by the optical control system of the present invention.Thus the optimum control of the foregoing processes can be achieved.

Since the spatial intensity distribution on a target and radiation timeintervals of the laser beam can be properly controlled through thegeneration of x-rays by irradiating a target with a laser beam producedby the optical control of the present invention, the process can beminutely designed.

The wavelength characteristic, namely, the intensity characteristic, ofx-rays may be measured and the intensity distribution and spatialoptical phase distribution of a laser beam may be adjusted on the basisof the measured wavelength characteristic of x-rays of a desiredwavelength. Preferably, the thus generated x-rays contain a largequantity of a proper wavelength component desired by the use of thegenerated x-rays. The intensity of x-rays of a desired wavelength may bemeasured and the spatial intensity distribution and the spatial opticalphase distribution can be adjusted so that the intensity of thewavelength component may be high.

In a laser plasma x-ray generator, it is preferable that the spatialintensity distribution and pattern of a spot formed by focusing a laserbeam on a part of a target correspond to a spatial light intensitydistribution in which the energy of the leading end of a light pulsefirst arriving at the target is concentrated on a part corresponding tothe center of an optical axis, and the spatial intensity distributionsof a series of light pulses subsequently reaching the target are beamshaving diameters that increase as a laser plasma expands and havingannular spatial distributions having a central part of a low lightintensity and a peripheral part of a high light intensity. When thelaser light pulses falling on the target have the foregoing spatialdistribution and phase distribution, a laser plasma can be held at aelectron temperature suitable for generating x-rays of a specificwavelength for a long time in a wide spatial region and x-rays of thedesired wavelength can be efficiently generated.

The optical control system of the present invention is capable ofgenerating a light wave having wavelength components having differentpredetermined spatial intensity distribution patterns by transforming alaser beam. Therefore, the light wave can be applied to anultrahigh-resolution scanning laser fluorescence microscope of the STEDsystem. A wavelength component of the same wavelength as a fluorescentlight wave in a specimen in a broad-band spectrum is selected from abroad-band spectrum and is used for fluorescence suppression, andwavelength components of other wavelengths are used as fluorescenceexcitation light waves. Since the fluorescence excitation light wavesand the fluorescence suppression light wave can be generated by thesingle optical system, the optical control system is simple.

An optical control method of the present invention includes the stepsof: making a linearly polarized light wave containing a plurality ofwavelength components fall on an optical rotatory device having anoptical rotatory dispersion characteristic to determine differentpolarization angles for the wavelength components, respectively; passingthe linearly polarized light wave passed through the optical rotatorydevice through a spatial light modulator to give an optical rotationangle to the entrance surface or optical rotation angles to parts of anentrance surface; and passing the linearly polarized light wave passedthrough the spatial light modulator through an analyzer to emit anoutgoing light wave containing wavelength components respectively havingcontrolled spatial light intensity distributions.

The optical control method may make a linearly polarized light wavecontaining the plurality of wavelength components fall on an azimuthrotator having an optical rotatory dispersion characteristic to givedifferent polarization angles to the wavelength components,respectively; may pass the linearly polarized light wave passed throughthe azimuth rotator through a spatial optical phase modulator to changethe spatial optical phase of the incident light wave on the entrancesurface or the spatial optical phases of the incident light wave onparts of the entrance surface; and may emit an outgoing light wavecontaining wavelength components having controlled spatial lightintensity distributions.

The optical control method of the present invention may include the stepof adjusting the optical phases of the wavelength components by awavelength phase modulator.

The phases, and the spatial light intensity distributions or the spatialoptical phase distributions of the wavelength components of the outgoinglight wave can be controlled by adjusting the optical phases of thewavelength components by the wavelength phase modulator simultaneouslywith the adjustment of spatial light intensities by the optical rotatorydevice, the spatial light modulator and the spatial optical phasemodulator.

The optical control method may focus the outgoing light wave by afocusing optical system disposed so that the outgoing light wave mayfall thereon.

The optical control method of the present invention can be applied tovarious illuminating methods, light sources for displays and processcontrol methods by using the effect of combination of the wavelengthcomponents respectively having different spatial distributions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an optical control system in a firstembodiment according to the present invention;

FIG. 2 is a graph showing the coefficient of chromatic dispersion ofoptical rotation angle in bismuth-iron garnet for wavelength;

FIG. 3 is a graph showing the dependence of optical rotation angle in aTN liquid crystal on voltage;

FIG. 4 is a diagrammatic view showing typical examples of opticalrotation angle patterns;

FIG. 5 is a view of assistance in explaining the concept of givingwavelength components different spatial light intensity distributions bya spatial light modulator included in the optical control system in thefirst embodiment;

FIG. 6 is a block diagram of assistance in explaining a method ofcontrolling the spatial light intensities of wavelength components bythe optical control system in the first embodiment including a spatiallight modulator;

FIG. 7 is a block diagram of assistance in explaining a control methodto be carried out by an optical control system built by additionallyproviding the optical control system in the first embodiment with apolarizer;

FIG. 8 is a view of assistance in explaining the operations of anoptical rotatory dispersion device and an analyzer;

FIG. 9 is a three-dimensional diagram of a Gaussian distribution typenear field pattern in an example when the spatial distribution ofpolarization plane optical rotation angle is controlled by the firstembodiment;

FIG. 10 is a three-dimensional diagram of a far field patterncorresponding to the near field pattern shown in FIG. 9 and obtainedthrough simulation;

FIG. 11 is a sectional view of a near field pattern in another example;

FIG. 12 is a sectional view of a far field pattern corresponding to thenear field pattern shown in FIG. 11;

FIG. 13 is a sectional view of a near field pattern in a third example;

FIG. 14 is a sectional view of a far field pattern corresponding to thenear field pattern shown in FIG. 14;

FIG. 15 is a three-dimensional diagram of a sectional profile of a nearfield pattern;

FIG. 16 is a three-dimensional diagram of a sectional profile of a farfield pattern corresponding to the near field pattern shown in FIG. 15;

FIG. 17 is a three-dimensional diagram of a near field pattern ofprimary Bessel function type when spatial distribution of polarizationangles is controlled by the first embodiment;

FIG. 18 is a three-dimensional diagram of a far field patterncorresponding to the near field pattern shown in FIG. 17 and obtainedthrough simulation;

FIG. 19 is a block diagram of an optical control system in a secondembodiment according to the present invention;

FIG. 20 is a diagrammatic view of a Fourier light synthesis opticalsystem;

FIG. 21 is a block diagram of assistance in explaining operations of theoptical control system in the second embodiment;

FIG. 22 is a block diagram of an optical control system in amodification of the optical control system in the second embodiment;

FIG. 23 is a block diagram of assistance in explaining operations of anoptical control system in a third embodiment according to the presentinvention;

FIG. 24 is a diagrammatic view of assistance in explaining the principleof forming a far field pattern from a near field pattern by a focusingoptical system;

FIG. 25 is a three-dimensional diagram of a near field pattern formed bythe third embodiment when an incident light wave is a plane wave;

FIG. 26 is a three-dimensional diagram of assistance in explaining phaserotation exerted on the incident light wave shown in FIG. 25;

FIG. 27 is a three-dimensional diagram of a far field patterncorresponding to the near field pattern shown in FIG. 25;

FIG. 28 is a sectional view of a section of the far field pattern shownin FIG. 27 in a plane including the axis of the far field pattern shownin FIG. 27;

FIG. 29 is a sectional view of a far field pattern when the polarizationangle of an incident light wave fallen on the optical control system inthe third embodiment is 20°;

FIG. 30 is a sectional view of a far field pattern when the polarizationangle of an incident light wave fallen on the optical control system inthe third embodiment is 90°;

FIG. 31 is a three-dimensional diagram of another near field patternformed by the optical control system in the third embodiment;

FIG. 32 is a three-dimensional diagram of a far field patterncorresponding to the near field pattern shown in FIG. 31;

FIG. 33 is a three-dimensional diagram showing the variation of a nearfield pattern of Gaussian function distribution type with thepolarization angle of an incident light wave;

FIG. 34 is a three-dimensional diagram of a far field pattern formed byfocusing the near field pattern shown in FIG. 33 by a focusing opticalsystem on the focal point of the focusing optical system;

FIG. 35 is a block diagram of an optical control system in a fourthembodiment according to the present invention;

FIG. 36 is a bock diagram of an optical control system in a fifthembodiment according to the present invention;

FIG. 37 is a block diagram of the optical control system shown in FIG.36 including a spatial optical phase modulator;

FIG. 38 is a block diagram of an optical control system in a fifthembodiment according to the present invention;

FIG. 39 is a block diagram of the optical control system shown in FIG.38 including a spatial optical phase modulator;

FIG. 40 is a diagram of assistance in explaining change of laser plasmaelectron temperature when an optical control system in a sixthembodiment according to the present invention is used;

FIG. 41 is a diagrammatic view of assistance in explaining the mechanismof an ultrahigh-resolution scanning laser fluorescence microscope(STED); and

FIG. 42 is a diagrammatic view of a STED in a seventh embodimentaccording to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will be described withreference to the accompanying drawings.

First Embodiment

An optical control system 11 in a first embodiment according to thepresent invention receives an incident linearly polarized light wavecontaining a plurality of wavelength components, passes the linearlypolarized light wave through an optical rotatory dispersion device tochange the polarization plane rotation angles of the wavelengthcomponents, passes the linearly polarized light wave through ananalyzer, and obtain a light wave containing wavelength componentsrespectively having different spatial light intensity distributions by aspatial light modulator including a polarization plane rotator, such asa liquid crystal.

Referring to FIG. 1, the optical control system 11 includes a wavelengthdispersion type optical rotatory device 3, an analyzer 7 and a spatiallight modulator 5 capable of giving an optional polarization anglespatial distribution to the polarization plane of the incident lightwave.

The analyzer 7 is an optical element that transmits a polarizedcomponent of a specific direction selectively. A representative exampleof the analyzer 7 is a polarizing plate, or a polarization beamsplitter. The analyzer 7 gives a spatial light intensity distribution toan outgoing light wave on the basis of an polarization angle determinedby the optical rotatory device 3.

The optical rotatory device 3 rotates the polarization plane of anincident light wave 1 through an polarization angle dependent on thewavelength of the incident light wave 1. Although the optical rotatorydevice 3 may be made of a natural optically rotatory material, such asquartz or a cholesteric liquid crystal, it is preferable that theoptical rotatory device 3 is a Faraday rotator because the naturaloptically rotatory material has a large optical rotation angle andcauses a large wavelength dispersion with optical rotation. When amagnetic field is applied to the Faraday rotator in a direction parallelto the optical axis of the Faraday rotator, the Faraday rotator exhibitsa rotatory characteristic proportional to the strength of the magneticfield. The Faraday rotator is easy to adjust. When an optical rotatorydevice 3 is made of a magnetic material, the rotatory characteristic ofthe optical rotatory device 3 is proportional to magnetization insteadof to the strength of a magnetic field. The present invention employs abismuth-iron garnet crystal (Bi₃Fe₅ crystal) having a particularly highoptical rotation angle deviation with wavelength.

FIG. 2 is a graph showing the chromatic dispersion coefficient of abismuth-iron garnet crystal, in which wavelength is measured on thehorizontal axis and polarization angle is measured on the vertical axis.The Faraday rotator using a bismuth-iron garnet crystal has a largewavelength dispersion coefficient and a large Faraday rotationcoefficient. Therefore, the Faraday rotator has a short transmissiondistance, permits the use of a smaller element and hence can reducelight transmission loss. For example, when a light wave of a wavelengthin the range of 700 to 800 nm is transmitted by a magnetically saturatedbismuth-iron garnet crystal, the difference in the direction ofpolarization plane between the upper and the lower end is as large asabout 18,000° per centimeter. Therefore, if the thickness of thebismuth-iron garnet crystal is 50 μm, the polarization angle dispersionis on the order of 90°.

The spatial light modulator 5 is divided into many cells. The cells ofthe spatial light modulator 5 individually give optional, rotationangles to the polarization plane of the linearly polarized light wave. Arepresentative example of the spatial light modulator 5 is a TN liquidcrystal device using the TN effect of a nematic liquid crystal.

Basically, the TN liquid crystal device is formed by sandwiching anematic liquid crystal layer of a thickness on the order of 10 μmbetween paired transparent electrodes. An optical rotation angle to begiven to the linearly polarized light wave transmitted by the TN liquidcrystal device is adjusted through the adjustment of the voltage appliedacross the transparent electrodes.

FIG. 3 is a graph showing the dependence of the optical rotation anglegiven to the incident linearly polarized light wave transmitted by theTN liquid crystal device on the voltage applied across the transparentelectrodes. When the voltage is varied between 3 V and 8 V, the opticalrotation angle varies between 0° and 90°. The cells arranged in linesand rows in a two-dimensional plane of the spatial light modulator 5 candetermine different optical rotation angles individually for thetransmitted light wave.

Thus an optional optical rotation angle pattern can be formed on atwo-dimensional space on which the linearly polarized light wave falls.

FIG. 4 shows a typical example of a thus formed optical rotation anglepattern. FIG. 4(a) shows a binary distribution of optical rotationangles when some of the cells arranged in a two-dimensional space rotatethe polarization plane of the transmitted light wave through an angle of90° while others of the cells do not rotate the polarization plane ofthe transmitted light wave. FIG. 4(b) shows a half-tone distribution ofoptical rotation angles, in which optical rotation angles provided bythe inner cells nearer to the center of the two-dimensional space arelarger and optical rotation angles provided by the outer cells fartherfrom the center of the two-dimensional space are smaller. Thus thepattern of optical rotation angles can be optionally adjusted byadjusting voltages applied to the cells.

The optical control system 11 shown in FIG. 1 passes an incident lightwave 1, namely, a linearly polarized light wave containing a pluralityof wavelength components, through the wavelength dispersion type opticalrotatory device 3 to give different polarization plane angles to thewavelength components, respectively, and illuminates the spatial lightmodulator 5 with the light wave 1 passed through the optical rotatorydevice 3. Since the cells on the entrance surface of the spatial lightmodulator 5 are set for different polarization plane angles,respectively, the spatial light modulator 5 adds the polarization planeangles to the polarization plane angles of the wavelength components ofthe linearly polarized light wave 4. Polarized components of thepolarized light wave emerging from the spatial light modulator 5 andparallel to the transmission polarization plane angle of the analyzer 7pass through the analyzer 7 and emerge from the optical control system11 as an outgoing light wave 8.

Suppose that the linearly polarized light wave 1 contains red, green andblue wavelength components, the optical rotatory device 3 givesdifferent inclinations of polarization planes to the red, green and bluewavelength components. The red, green and blue wavelength componentshaving polarization planes respectively having the differentinclinations fall on the spatial light modulator 5. Then, the cells ofthe spatial light modulator 5 give different optical rotation anglesrespectively to the wavelength components. Therefore, when the cells areset for optical rotation angles corresponding to the polarization planeangles of the red, green and blue wavelength components, respectively,the red, green and blue wavelength components form differenttwo-dimensional shapes, respectively, as shown in FIG. 5.

Since the analyzer 7 passes wavelength components parallel to thetransmission polarization plane angle, some wavelength components passthrough the analyzer 7 unless the polarization planes of the wavelengthcomponents are perpendicular to the inclination of the polarizationplane relevant to the spatial light modulator 5. In FIG. 5, therespective polarization angles of the red and the blue wavelengthcomponent are perpendicular to each other and hence the analyzer 7 isable to separate the red and the blue wavelength component completely.Since the polarization plane angle of the green wavelength componentdiffers by 45° from the polarization plane angles of the red and theblue wavelength component, the green wavelength component cannot becompletely separated from the red and the blue wavelength component.

The spatial light modulator 5 is divided into the plurality of cells andthe cells rotate the polarization planes of the linearly polarized lightwave individually through optionally different angles, respectively.Therefore, various spatial light intensity patterns can be formed forthe plurality of wavelength components by adjusting voltages appliedrespectively across the pairs of transparent electrodes of the cells orby adjusting the wavelength dispersion angle of the wavelengthdispersion type optical rotatory device 3.

FIG. 6 is a block diagram of assistance in explaining a method ofcontrolling the spatial light intensities of wavelength components bythe spatial light modulator 5 included in the optical control system 11.

Data signals 23 provided by sensors 21 and indicating a pressure, atemperature and light intensities of specific wavelength components aregiven to a controller 22. The controller 22 examines the data signals23, generates a control signal 24 on the basis of the data signals 23and gives the control signal 24 to a driver for driving the spatiallight modulator 5. The spatial light modulator 5 adjusts opticalrotation angles on the basis of the control signal 24.

The spatial light modulator 5 may be either a device having a singledivision having a uniform two-dimensional spatial distribution and adevice having a plurality of divisions respectively having individuallyadjustable optical rotation angles. The outgoing light wave 8 emergingfrom the optical control system 11 has a spatially uniform lightintensity and a spatially uniform color characteristic when the spatiallight modulator 5 has a plurality of divisions or the outgoing lightwave 8 emerging from the optical control system 11 has wavelengthcomponents respectively having different spatial light intensitydistributions and different spatial color characteristic distributionswhen the spatial light modulator 5 has a plurality of divisions.

When the azimuth rotator 3 of the optical control system 11 givesdifferent polarization angles to the wavelength components, the colorcharacteristic of the outgoing light wave 8 and the light intensities ofthe wavelength components can be adjusted by changing the ratios of thepolarization angle components for the wavelength components that passthrough the analyzer 7 by the spatial light modulator 5. Therefore, theoptical rotatory device 3 does not need to be a complicated device thatrequire the adjustment of optical rotation angle and may be a devicehaving a fixed strength of magnetization and a selectively determined,fixed thickness.

For example, when the incident light wave is a linearly polarized lightwave containing red, green and blue wavelength components, thewavelength optical rotation angle dispersions, namely, the differencesin optical rotation angle, of the red and the blue wavelength componentscan be adjusted to 90° and the wavelength dispersion of the greenwavelength component can be adjusted to 45°. If optical rotation anglesare set for the divisions of the spatial light modulator 5,respectively, so that the difference is 90°, the spatial light intensitydistributions of the red and the blue wavelength components contained inthe outgoing light wave have inverted patterns and the green wavelengthcomponent has a uniform spatial light intensity distribution.

The wavelength dispersion angle of the wavelength dispersion typeoptical rotatory device 3 and the polarization plane rotation angles ofthe divisions of the spatial light modulator 5 can be optionally set.Therefore, an optimum combination of spatial light intensitydistributions for the wavelength components can be selectivelydetermined, taking into consideration the power spectrum of the lightwave incident on the optical control system 11 and the adjustment of thephases of the wavelength components when the optical control system 11is applied to a practical use.

The optical control system 11 receives the incident light wave 1, i.e.,the linearly polarized light wave containing the plurality of wavelengthcomponents, passes the incident light wave 1 through the azimuth rotator3 having an optical rotatory dispersion characteristic for wavelength tochange the polarization [plane rotation angles of the wavelengthcomponents, and passes the incident light wave 1 emerging from theoptical rotatory device 3 through the spatial light modulator 5including a polarization plane rotator, such as a liquid crystal, toprovide the outgoing light wave 8 having wavelength componentsrespectively having different spatial light intensity distributions.

FIG. 7 is a block diagram of assistance in explaining a control methodto be carried out by an optical control system 12 built by additionallyproviding the optical control system 11 with a polarizer 6. Anoptionally polarized incident light wave 2 is used instead of thelinearly polarized light wave 1 emitted by a laser. The polarizer 6transmits only a specific linearly polarized light wave component of theincident light wave 2. Therefore, an outgoing light wave 8 emerging froman analyzer 7 and having wavelength components respectively havingdifferent spatial light intensities can be provided by a mechanism shownin FIG. 8.

The optical control system 11 provided with the polarizer 6 has agreatly increased degree of freedom of selection of the incident lightwave and can process any one of light waves emitted by an incandescentlamp, a fluorescent lamp, an electroluminescent light source and alight-emitting diode.

The light wave emitted by a light source may have any one of continuousspectra, like that of white light, and line spectra or may be a lightwave containing red, green and blue wavelength components. The incidentlight wave may be any one of coherent light waves, incoherent lightwaves and partially coherent light waves.

The light wave produced by the optical control system in this embodimenthas wavelength components respectively having different spatial patternsand different light intensity distributions which are easily andcontinuously controllable.

Accordingly, the optical control system in this embodiment can beapplied to the illumination of advertising pillars, exhibition halls,stages, fountains, restaurants, shops, game machines, controllers offactories and power plants, and traffic facilities, such as automobiles,railways, ships and aircrafts, and can be used as light sources fordisplays.

The optical control system can be applied to uses for directly observingthe outgoing light wave at the exit surface of the optical controlsystem. The outgoing light wave emerging from the optical control systemcan be focused on a focal point of a focusing optical system by thefocusing optical system to use the spatial and temporal energydistributions of the outgoing light wave.

A light wave containing wavelength components respectively havingdifferent spatial light intensity distributions appear on the exitsurface of the optical control system and forms a near field pattern.The outgoing light wave emerging from the optical control system form anoptical intensity distribution corresponding to the near field pattern,namely, a far field pattern, on a predetermined arrival plane due to thepropagation and interference of light wave components emerging from theexit surface of the spatial light modulator 5 according to theHuygens-Fresnel principle. The far field pattern represents the actionof light energy

Therefore, when the relation between the near field pattern and the farfield pattern is determined and the optical components are adjusted sothat a near field pattern corresponding to a desired far field patterncan be formed, a desired energy distribution can be formed at a point ofapplication.

The relation between a near field pattern and a far field pattern can bedetermined through simulation.

FIGS. 9 to 18 are diagrams showing results of simulation of the relationbetween a near field pattern and a far field pattern when anpolarization plane angle spatial distribution is controlled.

It was supposed for simulation that an incident light wave, namely, alinearly polarized light wave, is projected on a 2 cm-square areathrough a round opening of 2 cm in diameter and the area was dividedinto 100×100 divisions.

The polarization angle of the linearly polarized light wave with respectto a reference axis parallel to one side of an operation area ismeasured. The polarization angle is determined by the optical rotatorydispersions of the wavelength components caused by an azimuth rotator.

Suppose that a Gaussian distribution function is expressed by:$A = \exp^{- \frac{r^{2}}{B^{2}}}$where A is the amplitude of the light wave, r is distance from theoptical axis (=(x²+y²)^(1/2)), and B(=0.5) is a shape parameter.

Suppose that a near field pattern is represented by a three-dimensionalGaussian distribution shown in FIG. 9 when the polarization angle is 0°.Then, a far field pattern represented by a Gaussian distribution havinga narrow half width as shown in FIG. 10 can be formed.

When a linearly polarized light wave having an polarization angle of 45°forms a near field pattern of a three-dimensional Gaussian distributionhaving a section in a plane containing the optical axis as shown in FIG.11, a far field pattern having a three-dimensional Gaussian distributionhaving a section in a plane containing the optical axis as shown in FIG.12. The section shown in FIG. 12 has a high light intensity peak on theoptical axis and low light intensity peaks on the opposite sides of theoptical axis.

When a linearly polarized light wave having an polarization angle of 90°forms a near field pattern of a three-dimensional Gaussian distributionhaving a section in a plane containing the optical axis and having alight intensity of zero on the optical axis as shown in FIG. 13, a farfield pattern having a light intensity distribution having a peak on theoptical axis as shown in FIG. 14 is formed.

FIG. 15 is a three-dimensional picture obtained by continuously plottingthe profile of the section of the near field pattern shown above withrespect to polarization angle. It was found that the sharpness of a peakon the optical axis of a far field pattern corresponding to those nearfield patterns increases as polarization angle increases as shown inFIG. 16.

Since the optical rotatory dispersion device changes polarization angleaccording to wavelength, the formation of a near field pattern thatchanges according to polarization angle signifies changing a near fieldpattern according to wavelength. Thus a far field pattern formed on thebasis of a near field pattern that changes according to polarizationangle changes according to wavelength.

FIGS. 17 and 18 show a near field pattern and a far field pattern,respectively. The spatial modulation of the near field pattern shown inFIG. 17 has a distribution expressed by a primary Bessel function. Thefar field pattern corresponding to the near field pattern has an annularshape.

Light intensity I in a Bessel function distribution is expressed by;I=I ₀(2J ₁(r)/r−ε ²×2J ₁(εr)/εr)²where r is distance from the optical axis, ε is parameter of the radiusof a shading plate meeting an inequality: 0<ε<1 and J₁ is primary Besselfunction.

When the near field pattern shown in FIG. 17 is formed, the far fieldpattern has the shape of a doughnut as shown in FIG. 18.

When the relation between the near field pattern and the far fieldpattern is known previously, a desired far field pattern can be formedby forming a proper near field pattern, i.e., a spatial light intensitydistribution, on the exit surface of the optical control system. Adesired optical reaction can be caused by irradiating an object withlight energy having a predetermined spatial light intensitydistribution.

Second Embodiment

An optical control system 13 in a second embodiment according to thepresent invention is provided with a wavelength phase modulator 17 inaddition to components corresponding to those of the optical controlsystem 11. The optical control system 13 adjusts, in addition to spatiallight intensity distributions of wavelength components, the temporalwaveform or phases of wavelength components of an incident light wave toemit a desired outgoing light wave.

Referring to FIG. 19 schematically showing the optical control system 13in the second embodiment, the optical control system 13 adjusts thephases of the wavelength components of an incident linearly polarizedlight wave 1 so as to meet a predetermined relation by the wavelengthphase modulator 17, changes the polarization plane rotation angles ofthe wavelength components by an azimuth rotator 3 having an opticalrotatory dispersion characteristic, and then passes the incidentlinearly polarized light wave 1 processed by the wavelength phasemodulator 17 and the azimuth rotator 3 through an analyzer 7 to emit anoutgoing light wave 8 having wavelength components respectively havingdifferent spatial light intensities and different phases.

The wavelength phase modulator 17 is, for example, a pulse shapingoptical system called a Fourier light synthesis system. FIG. 20 is adiagrammatic view of the Fourier light synthesis system.

The Fourier light synthesis system includes an entrance diffractiongrating 18, an entrance focusing optical system 19, a spatial lightmodulator 20 capable of spatial modulation, an exit focusing opticalsystem 19′ and an exit diffraction grating 18′. The Fourier lightsynthesis system is an ultrashort light pulse Fourier shaping systemformed by arranging two sets each of a diffraction grating and a lens onthe opposite sides of the spatial light modulator 20, respectively, atintervals corresponding to focal distance in a 4-f arrangement.

The spatial light modulator 20 uses, for example, an array type liquidcrystal light modulator, for controlling the optical path length oftransmitted light. The spatial light modulator 20 is capable ofindividually adjusting the respective optical path lengths of opticalcomponents of incident light separated in a direction perpendicular tothe optical axis; that is, the spatial light modulator 20 is capable ofadjusting the phases of the wavelength components of an incident lightwave to predetermined phases by changing the respective optical pathlengths of the wavelength components separated by spectral resolution.

An incident light wave 1 having a plurality of wavelength components,such as an ultrashort light pulse, is subjected to angular dispersion bythe entrance diffraction grating 18 and is transferred to a Fouriertransform plane by the focusing optical system 19 disposed in a Fouriertransform arrangement. The wavelength components are arranged linearlyin parallel beams in a direction perpendicular to the optical axis onthe Fourier transform plane by spectral development. The respectivephases of the wavelength components are delayed or the respectiveamplitudes of the wavelength components are reduced by a spatial lightmodulator 5 placed on the Fourier transform plane. The light wave 1passed through the spatial light modulator 5 is subjected to opticalinverse Fourier transform. Consequently, a light pulse 4 emerging fromthe exit diffraction grating 18′ has wavelength components respectivelyhaving individually adjusted phases. Thus the light pulse 4 isequivalent to a light wave produced by temporal phase modulation.

The light wave is passed through an optical rotatory device 3 and ananalyzer 7 to adjust the spatial light intensity thereof. An outgoinglight wave 8 processed by temporal phase and amplitude adjustmentemerges from the optical control system 13.

The Fourier light synthesis optical system is capable of effectivelyadjusting the phases of the individual wavelength components of anultrashort pulse of femtoseconds. The aforementioned AOPD, as comparedwith the Fourier light synthesis optical system, is effective in dealingwith a slower phenomenon. Although the optical control system 13 hasbeen described on an assumption that the light wave has red, green andblue wavelength components for simplicity, naturally, the opticalcontrol system 13 is capable of separating the wavelength components ofa light wave having a continuous spectrum and modulating the phases ofthe wavelength components.

FIG. 21 is a block diagram of assistance in explaining operations of theoptical control system 13 in the second embodiment for individuallycontrolling the respective spatial light intensities of the wavelengthcomponents. The optical control system 13 can be applied to varioustypes of illumination, display and process control. Data signals 23provided by sensors 21 and indicating a pressure, a temperature andlight intensities of specific wavelength components are given to acontroller 22. The controller 22 examines the data signals 23, generatesa control signal 24 on the basis of the data signals 23 and gives thecontrol signal 24 to the wavelength phase modulator 17 and the azimuthrotator 3. Then, the wavelength phase modulator 17 adjusts therespective phases of the wavelength components and the optical rotatorydevice 3 changes the optical rotation angle.

Needless to say, the optical rotation angle may be adjusted by theanalyzer instead of or in addition to the optical rotation angleadjustment by the optical rotatory device 3.

FIG. 22 is a block diagram of an optical control system 15 in amodification of the optical control system 13 in the second embodiment.The optical control system 15 is provided, in addition to the componentsof the optical control system 13, a spatial light modulator 5 capable ofgiving an optional spatial optical rotation angle distribution to thepolarization plane of the incident light wave. The spatial lightmodulator 5 is interposed between the wavelength dispersion type azimuthrotator 3 and the analyzer 7.

The optical control system 15 shown in FIG. 22 passes an incidentlinearly polarized light wave 1 having a plurality of wavelengthcomponents through the wavelength phase modulator 17 to adjust therespective phases of the wavelength components, gives differentpolarization plane rotation angles to the wavelength components by thewavelength dispersion type optical rotatory device 3, adjusts thespatial distribution of the polarization plane rotation angle of theincident light wave by the spatial light modulator 5 to select a lightwave to be passed through the analyzer 7.

Thus the wavelength components of the outgoing light wave 8 aredetermined selectively and the respective light intensities of thewavelength components are adjusted to control the color characteristicand light intensity of the outgoing light wave 8 properly. Thus thetemporal relative positions of the wavelength components can be changed.The optical control system 15 has a wide variety of uses particularly ina field where light energy is used.

The optical control systems 13 and 15, similarly to the optical controlsystem 11 in the first embodiment, can use a linearly polarizedcomponent of an optional polarized light wave having optional wavelengthcomponents other than linearly polarized light waves by extracting thelinearly polarized component from the incident polarized light wave by apolarizer disposed at a position of incidence to use the linearlypolarized light wave.

In the optical control systems 13 and 15, the spatial light modulator 5changes the wavelength spatial light intensities, and the wavelengthphase modulator 17 has the ability of wavelength phase modulation. Thus,temporal waveform can be adjusted simultaneously with the preciseadjustment of the spatial light intensity distributions of thewavelength components. Thus the optical control systems 13 and 15 havingsimple construction including the several optical components can easilyachieve the precise temporal and spatial control of light. The abilityto achieve the precise temporal and spatial control of light of theoptical control system of the present invention is very useful inprocess control using light.

Third Embodiment

An optical control system 51 in a third embodiment according to thepresent invention forms a desired far field pattern by adjusting a nearfield phase distribution by using a spatial light modulator capable ofcontrolling spatial optical phase to achieve laser process control.

Referring to FIG. 23 showing the optical control system 51, the opticalcontrol system 51 has a wavelength dispersion type optical rotatorydevice 3 capable of changing optical rotation angle according towavelength and a spatial optical phase modulator 52. An incident lightwave 1 passes through the optical rotatory device 3 and the spatialoptical phase modulator 52 in that order.

The spatial optical phase modulator 52 produces an outgoing light wave53 differing in the ratio between a polarized component to be subjectedto spatial optical phase modulation and a polarized component not to besubjected to spatial optical phase modulation from a light wave having adifferent polarization plane angle by individually and spatiallychanging only one of polarized components, parallel to one of twoperpendicularly intersecting coordinate axes defining a planeperpendicular to an optical axis. For example, the spatial optical phasemodulator 52 is a two-dimensional optical phase modulator using theanisotropic refraction index of a nematic liquid crystal. The nematicliquid crystal has elongate molecules and has an refractive indexanisotropy having an extraordinary ray axis subject to phase delay in adirection parallel to the major axes of the molecules and an ordinaryray axis not subject to phase delay in a direction perpendicular to thedirection parallel to the major axes of the molecules.

The two-dimensional optical phase modulator is a nematic liquid crystaldevice in which molecules of a nematic liquid crystal are arranged alongthe optical axis with the axes thereof extended parallel to a directionperpendicular to the optical axis. The liquid crystal molecules of theliquid crystal device are oriented in a direction defined by anorientation film while any electric field is not applied thereto.

When a voltage is applied across transparent electrodes sandwiching aliquid crystal layer, the axes of the liquid crystal molecules areinclined to the optical axis according to the applied voltage to changethe phase of a polarized light wave polarized in the direction of theaxes of the molecules. The phase of a polarized light wave polarized ina direction perpendicular to the axes of the liquid crystal moleculesdoes not change even if the position of the axes of the liquid crystalmolecules changes.

The ratio between a first polarized component parallel to the major axesof the liquid crystal molecules and a second polarized componentperpendicular to the major axes of the liquid crystal molecules of theincident linearly polarized light wave is dependent on the direction ofpolarization. Therefore, phase delay is dependent on the angle of thepolarization plane of the incident polarized light wave. Phase delay isdependent on the voltage applied across the transparent electrodes.

Proper voltages are applied to two-dimensional positions on the spatialoptical phase modulator to form a predetermined phase delay pattern, anda linearly polarized light wave having a plurality of wavelengthcomponents is passed through the azimuth rotator. Then, differentpolarization plane optical rotation angles are given to the wavelengthcomponents of the incident linearly polarized light wave, respectively.Then, the linearly polarized light wave falls on the spatial opticalphase modulator on which the two-dimensional phase delay pattern isformed. Different phase differences are given to the light wave emergingfrom the spatial optical phase modulator according to voltages setrespectively for positions on the entrance surface and according to thepolarization plane rotation angles given to the wavelength components.

When the optical control system 51 in the third embodiment receives alinearly polarized light wave 1, the optical rotatory device 3 givesoptical rotation angles respectively to the wavelength components and alight wave 4 emerges from the optical rotatory device 3. The light wave4 falls on the spatial optical phase modulator 52 having entrancesurface having parts adjusted respectively to different phase changequantities. Since the wavelength components have polarization planes ofdifferent inclinations, respectively, only one of polarized components,parallel to one of two perpendicularly intersecting coordinate axes canbe individually and spatially changed. Thus the spatial optical phasemodulator 52 produces the outgoing light wave 53 having light wavecomponents respectively having different polarization plane angles anddifferent ratios between a polarized component to be subjected tospatial optical phase modulation and a polarized component not to besubjected to spatial optical phase modulation.

A near field phase distribution having different ratios between apolarized component subjected to spatial optical phase modulation and apolarized component not subjected to spatial optical phase modulation isformed on the exit surface of the spatial optical phase modulator 52. Alight intensity distribution corresponding to the near field phasedistribution, namely, a far field pattern, is formed on the focal planeof a focusing optical system by focusing the outgoing light waveemerging from the spatial optical phase modulator 52 by the focusingoptical system. The far field pattern shows the action of light energyon the focal plane.

FIG. 24 is a diagrammatic view of assistance in explaining the principleof forming the far field pattern from the near field pattern by thefocusing optical system.

An initial outgoing light condition can be indicated by projecting anear field light intensity distribution and a near field phasedistribution in the direction of the optical axis on a spherical surfaceof a radius f equal to the focal distance f of the focusing opticalsystem. Light projected on the spherical surface propagate according tothe Huygens-Fresnel principle and is focused on a space near the focalpoint to form a far field pattern.

The near field pattern and the far field pattern are correlated byFourier transform and Fourier inverse transform. A light intensitypattern can be formed at a position corresponding to the focal point byexactly determining the relation between the near field pattern and thefar field pattern on the basis of test results and simulation andforming a near field light intensity distribution corresponding to adesired far field pattern.

FIGS. 25 to 34 are diagrams formed through simulation to determine therelation of the near field pattern and the near field phase distributionwith the far field pattern by simulation.

The simulation was conducted on an assumption that a spatial lightintensity distribution having a central hole for a far field pattern isneeded and used a phase rotation beam processed by phase rotation by thespatial optical phase modulator so that the phase changes by 2π or by anintegral multiple of 27π when the near field pattern is turned one fullturn about the optical axis.

FIG. 25 is a three-dimensional diagram showing the optical intensitydistribution of a near field pattern when the incident light wave to theoptical control system 51 is a plane wave. The incident light wave has acircular distribution of 2 cm in diameter and has a light intensity of 1W/cm².

FIG. 26 is a three-dimensional diagram of assistance in explaining phaserotation exerted on the incident light wave. A phase rotation of 2π isexerted on the incident light wave about the optical axis.

FIG. 27 is a three-dimensional diagram of the light intensitydistribution of a far field pattern corresponding to the near fieldpattern shown in FIG. 25. FIG. 28 is a sectional view of a section ofthe far field pattern shown in FIG. 27 in a plane including the axis ofthe far field pattern shown in FIG. 27. The far field pattern has adoughnut shape having a central part on the optical axis having a lowlight intensity and a peripheral part at a distance from the opticalaxis and surrounding the optical axis and having a high light intensity.

FIG. 29 is a sectional view of a far field pattern when the polarizationangle of an incident light wave is 20°. A reduction of the lightintensity of a central part on the optical axis is small because thepolarization angle is small. FIG. 30 is a sectional view of a far fieldpattern when the polarization angle of an incident light wave is 90°. Aconsiderably sharp peak appears in a central part on the optical axis.

FIG. 31 is a three-dimensional diagram of a section of a light intensitydistribution with respect to the axis of symmetry of a near fieldpattern for polarization angle as a parameter. The light intensity ofthe near field pattern is influenced by neither distance in thedirection of radius vector nor polarization angle.

FIG. 32 is a three-dimensional diagram of the light intensitydistribution of a far field pattern corresponding to the near fieldpattern shown in FIG. 31 for polarization angle as a parameter. Thelight intensity distribution has a low central part on the optical axisfor small polarization angles when the light intensity is the same, hasa peak on the optical axis for a large polarization angle and thesharpness of the peak increases as the polarization angle increases.

FIG. 33 is a three-dimensional diagram of a near field pattern of aGaussian function distribution type for the polarization angle of anincident light wave in the so-called phase rotation beam.

FIG. 34 is a three-dimensional diagram of a far field pattern formed byfocusing the near field pattern shown in FIG. 33 by a focusing opticalsystem on the focal point of the focusing optical system. The variationof the light intensity distribution of the far field pattern bears aclose resemblance to that of a light wave having a uniform intensitydistribution. A near field pattern of a Gaussian function distributiontype, as compared with a light wave having a uniform intensitydistribution, has a low wall and a low peak light intensity.

Since different light intensity patterns can be formed for differentpolarization angles, various light energy patterns can be formed byusing a linearly polarized light wave having a plurality of wavelengthcomponents as an incident light wave to increase the degree of freedomof optical output control, such as laser process control.

The spatial light intensity distribution of a far field pattern can becontrolled with out passing the outgoing light wave through the analyzerwhen the spatial optical phase modulator is used. Consequently, lightenergy can be efficiently used without attenuating the light wave.

Since the polarization plane of an incident light wave incident on theoptical rotatory device can be selected by placing a polarizer above theoptical rotatory device or with respect to the direction of travel ofthe incident light wave, the same effect can be expected even if a lightwave other than the linearly polarized light wave is used.

A control mechanism, not shown, for controlling the spatial opticalphase modulator and the azimuth rotator, similarly to the opticalcontrol system in the first embodiment, receives data signalsrepresenting external conditions and provided by various sensors, sendsproper control signals produced on the basis of the data signals to thespatial optical phase modulator or the azimuth rotator to provide adesired outgoing light wave.

Thermal reactions, such as melting and evaporation, nuclear reactions,plasma reactions, chemical reactions and processes, such as isotopeseparation and fluorescent luminance, can be achieved by irradiatingmatters with laser pulses produced by the optical control system of thepresent invention and having a plurality of wavelength components andcontrolled temporal and spatial light pulse construction. Thoseprocesses can be applied to laser machining, synthesis, decompositionand separation of chemical substances and elements, production ofparticles, such as atoms, molecules, ions, electrons, positiveelectrons, neutrons and clusters, production electromagnetic radiations,such as x-rays and γ-rays, and production and control of fluorescentlight.

Those techniques are expected to be applied to the industrial fields ofsemiconductors, chemistry, energy, medicine and machinery, and basicstudies of particle accelerators and inspection of biologicalsubstances.

Fourth Embodiment

The foregoing optical control systems embodying the present inventioncan be used in combination with various light sources as shown in FIGS.35 to 39. An optical control system of the present invention applied tolaser plasma x-ray generation will be described.

Laser plasma x-rays are generated when a target, such as a metal piece,is irradiated with a short-pulse high intensity laser beam. A mechanismof x-ray generation from a laser plasma will be described. When a targetis irradiated with a laser beam, an irradiated part of the targetchanges into a plasma. Most part of the energy of the laser beam isabsorbed by the electrons of the plasma at an initial stage. Therefore,the plasma thus produced contains high-temperature electrons andlow-temperature ions the high-temperature electrons excite theinner-shell electrons of the ions. When the excited inner-shellelectrons relax to a lower energy level, x-rays of a wavelengthcorresponding to the level difference are radiated. The radiation ofx-rays continues while the electrons are kept at temperatures highenough to excite the inner-shell electrons of the ions.

Normally, electrons of the plasma are in a state of local thermalequilibrium and the state distribution of the electrons can beapproximated by a Boltzmann distribution. If the electron temperature isexcessively high, the electrons having energy more than that necessaryfor exciting the inner-shell electrons increase and, consequently, astate unsuitable for generating x-rays of a specific wavelength iscreated. If the electron temperature is excessively low, the number ofthe electrons having energy sufficient to excite the inner-shellelectrons decreases.

Therefore, there is an optimum electron temperature for the material ofthe target to make inner-shell electrons generate x-rays of a specificwavelength. Since there is an optimum temperature for generating x-raysof a specific wavelength, it is ideal that the control of laser plasmax-ray generation maintains an optimum electron temperature for thelongest possible time in the widest possible range.

FIG. 40 is a diagram of assistance in explaining the ideal temporaldevelopment of laser plasma electron temperature for generating x-raysof a specific wavelength, in which spatial extension is measured on thehorizontal axis and the light intensity distribution 32 of anirradiating laser beam and plasma electron temperature 33 are measuredon the vertical axis. It is preferable that the plasma electrontemperature 33 is maintained at an optimum temperature level 34 forx-ray generation while the plasma electron temperature 33 develops inthe order of FIGS. 40(a), 40(b) and 40(c).

In the laser plasma x-ray generator in this embodiment, it is preferablethat the leading end of a pulse of the laser beam that reaches thetarget first has a pattern of spatial light intensity distribution 32 asshown in FIG. 40(a) showing the concentration of energy on a centralpart of the optical axis and the spatial light intensity distributions32 of a series of pulses of the laser beam subsequently reaching thetarget expand following the expansion of the laser plasma as shown inFIGS. 40(b)and 40(c) and become an annular light intensity distributionhaving a central part of a low light intensity and a peripheral part ofa high light intensity.

The electron temperature 33 of the laser plasma can be maintained at theoptimum temperature level 34 for generating x-rays of a specificwavelength in a wider space for a longer time by making the pulses ofthe laser beam form the foregoing spatial light intensity distribution.Consequently, x-rays of a desired wavelength can be efficientlygenerated.

When a target is irradiated with a laser beam emitted by the opticalcontrol system in this embodiment to generate x-rays, the spatial lightintensity distribution of the laser beam at the position of the targetand the intervals of irradiation can be properly adjusted. Consequently,an x-ray generating process can be minutely designed. The opticalcontrol system in this embodiment having the optical system simpler thanthat of the conventional optical control system can achievesubstantially optimum laser plasma control and can precisely control thecharacteristics of the generated x-rays.

The wavelength characteristic as a strength characteristic of x-rays maybe measured, and the light intensity distribution of the laser beam andthe phases of the wavelength components may be adjusted on the basis ofthe measured light intensity of x-rays. Preferably, the generated x-rayshave many proper wavelength components required by the use of thex-rays. The light intensity of x-rays of a desired wavelength may bemeasured, and the spatial light intensity distribution and the phases ofthe wavelength components may be adjusted so that the desired wavelengthcomponent has a high light intensity.

Fifth Embodiment

The optical control system of the present invention is capable oftransforming a laser beam to generate a laser beam having wavelengthcomponents respectively having different spatial light strengthdistributions. The laser beam thus generated can be applied to anultrahigh-resolution scanning laser fluorescence microscope of a STEDsystem.

FIG. 41 is a diagrammatic view of assistance in explaining the mechanismof an ultrahigh-resolution scanning laser fluorescence microscope of aSTED system. STED stands for stimulated emission depletion.

A scanning laser fluorescence microscope of a STED SYSTEM has aresolution higher than that of an ordinary scanning laser fluorescencemicroscope. An excitation light 43 as a leading pulse is projected on afluorescence molecule excitation area 44 in a specimen, and an annularSTED light beam 45 as a succeeding pulse is projected coaxially with theexcitation light beam 43 on the specimen before a short time far shorterthan fluorescence lifetime passes after the excitation of fluorescentmolecules to suppress fluorescent light emission and a fluorescent lightbeam 46 of a size corresponding to the diameter of the central space ofthe annular STED light beam 45 is detected.

The scanning laser fluorescence microscope of a STED system can reducethe diameter of a scanning spot during observation to improve theresolution of the scanning laser fluorescence microscope of a STEDsystem.

The conventional scanning laser fluorescence microscope of a STED systemdivides an ultrashort-pulse laser beam into two divisional laser beamsafter adjusting the wavelength of the ultrashort-pulse laser beam by anoptical parametric amplifier (OPO), subjects one of the two divisionallaser beams to wavelength conversion by a second harmonic generation(SHG) to use the same as a source light beam for fluorescence excitationand synthesizes the other divisional laser beam coaxially with thefluorescence excitation light beam processed by wavelength conversion bySHG. Therefore, the conventional scanning laser fluorescence microscopeof a STED system needs a complicated optical system.

FIG. 42 is a diagrammatic view of an optical control system embodyingthe present invention applied to an laser fluorescence microscope of aSTED system.

The optical control system of the present invention in this applicationseparates a wavelength component of a wavelength equal to that offluorescent light emitted by a specimen from light emitted by a lightsource and having wavelength components in a wide spectrum, delays theseparated wavelength component to produce a STED light beam 45 thatsuppresses fluorescence by stimulated emission. The rest of thewavelength components are used as fluorescence excitation light 43.

The STED stimulated emission light beam is an annular beam and hence itis preferable to use a phase rotation beam. When a phase rotation beamis projected in one direction on a specimen, a torque acts on anobservation unit. Therefore, a phase rotation beam of opposite phaserotation is projected in the opposite direction simultaneously with theformer phase rotation beam.

An outgoing light beam 8 emerging from the optical control system of thepresent invention is collimated by a lens 35 and is divided into twohalf beams by a beam splitter 36. The two half beams travel two opticalpaths of the same optical path length, respectively, and are focused ona specimen 39 from opposite directions by two objectives 38,respectively.

Light emitted by the specimen 39 travels the optical paths in thereverse direction. The light emitted by the specimen 39 is focused bythe lens 35, the focused light is reflected by a dichroic mirror 40,travels through a pinhole 41 and falls on a detector 42.

The laser fluorescence microscope of a STED system in this embodimentcan provide two types of light beams, namely, the fluorescenceexcitation light beam 43 and the STED light beam 45 by the singleoptical system. Therefore, the fluorescence microscope of a STED systemof the present invention, as compared with the conventional fluorescencemicroscope of a STED system, is simple in construction, can be made at alow cost and is easy to handle.

INDUSTRIAL APPLICABILITY

The optical control system of the present invention continuously changesthe spatial light intensities of the wavelength components of a lightbeam and hence can easily change the color characteristic of an outgoinglight beam so that the outgoing light beam has a desired colorcharacteristic selected from various color characteristics. Thus thelight beam emerging from the optical control system can be used byvarious illumination devices and various displays. Thus the opticalcontrol system promotes the use of light in various industries.

Since the spatial intensity distribution and temporal waveform of alaser light pulse can be continuously and minutely adjusted, the highlyaccurate control of a laser reaction process can be achieved. Thus theoptical control system of the present invention promotes the use oflight in various industries.

When the x-ray generator of the present invention is used for radiatingx-rays by producing a plasma with a laser beam, the intensity of thex-rays can be adjusted and, particularly, the intensity of x-rays of aspecific wavelength can be selectively adjusted. When the presentinvention is applied to an ultrahigh-resolution microscope of a STEDsystem, the single optical system can produce a fluorescence excitationlight beam and a STED light beam. Thus the optical control system of thepresent invention has simple construction.

1-26. (canceled)
 27. An optical control system comprising: an opticalrotatory device having an optical rotatory dispersion characteristicthat changes optical rotation angle according to wavelength; and aspatial optical phase modulator having an entrance surface capable ofcontrolling the wave surface of an incident light wave or an entrancesurface having parts capable of individually controlling the wavesurface of an incident light wave to adjust the spatial phasedistribution of the incident light wave; wherein the incident light wavepasses the optical rotatory device and the spatial optical phasemodulator in that order, the optical rotatory device transmits anincident linearly polarized light wave containing a plurality ofwavelength components and gives optical rotation angles respectively tothe wavelength components, the linearly polarized light wave passedthrough the optical rotatory device is passed through the spatialoptical phase modulator with an entrance surface having an spatialoptical phase modulation degree or with an entrance surface having partsadjusted respectively to spatial optical phase modulation degrees, thespatial optical phase modulator produces an outgoing light wave havingadjusted ratios of light quantities subject to spatial optical phasemodulation for the wavelength components, and the wavelength componentsform different far field patterns, respectively.
 28. The optical controlsystem according to claim 27, wherein the spatial optical phasemodulator is a two-dimensional optical phase modulator that modulatesthe phase of only a polarized light component polarized in a directionparallel to one of two perpendicularly intersecting coordinate axesdefining a plane perpendicular to the optical axis of the incident lightwave.
 29. The optical control system according to claim 27, wherein thespatial optical phase modulator is a parallel oriented nematic liquidcrystal spatial light modulator.
 30. The optical control systemaccording to claim 27, wherein the azimuth rotator gives differentpolarization angles respectively to the polarized wavelength componentsof the incident light wave by using an optically rotatory dispersioneffect to emit a light wave having different ratios between twopolarized components distributed along perpendicularly intersectingreference coordinate axes contained in a plane perpendicular to theoptical axis for the wavelength components, and the spatial opticalphase modulator receives the light wave emerging from the azimuthrotator and emits an outgoing light wave having an adjusted ratiobetween polarized components undergone spatial phase modulation andhaving light surfaces having shaped spatial shape and polarizedcomponents not undergone spatial phase modulation and having wavesurfaces having unchanged spatial shapes.
 31. The optical control systemaccording to claim 27, wherein the spatial phase modulating action ofthe spatial light modulator forms a spiral spatial optical phasedistribution in the outgoing light wave and a phase shift for one fullturn about the optical axis is approximately equal to an integralmultiple of 2π rad.
 32. The optical control system according to claim 27further comprising a wavelength phase modulator capable of adjusting therespective optical phases of the wavelength components.
 33. The opticalcontrol system according to claim 32, wherein the adjusting operation ofthe wavelength phase modulator for the adjustment of the optical phasesof the wavelength components is performed simultaneously with theadjusting operation the optical rotatory device, the spatial lightmodulator or the spatial optical phase modulator to control the phases,and the spatial light intensity distributions or spatial optical phasedistributions of the wavelength components of the outgoing light wavesimultaneously.
 34. The optical control system according to claim 27,wherein the effect of combination of the plurality of wavelengthcomponents of the outgoing light wave respectively having differentspatial distributions is applied to various process control purposes.35. The optical control system according to 34 wherein the laser plasmax-ray generating rate of a laser plasma x-ray generator is controlled bymaking the leading end of a light pulse first arriving at a target ofthe laser plasma x-ray generator have a spatial light intensitydistribution concentrating energy on a central part of the optical axis,and by making a series of light pulses subsequently reaching the targethave annular spatial distributions having a central part of a low lightintensity and a peripheral part of a high light intensity.
 36. Theoptical control system according to claim 34, wherein a wavelengthcomponent of the same wavelength as a fluorescent light wave in abroad-band spectrum is used for fluorescence suppression, and wavelengthcomponents of other wavelengths are used as fluorescence excitationlight waves in an ultrahigh-resolution scanning fluorescence microscopeof a STED system.
 37. An optical control method comprising the steps of:making a linearly polarized light wave containing a plurality ofwavelength components fall on an optical rotatory device having anoptical rotatory dispersion characteristic to give differentpolarization angles respectively to the wavelength components; passingthe linearly polarized light wave passed through the optical rotatorydevice through a spatial optical phase modulator to change the spatialoptical phase of the incident light wave on an entrance surface or thespatial optical phases of the incident light wave on parts of anentrance surface; and emitting an outgoing light wave containingwavelength components having controlled spatial light intensitydistributions.
 38. The optical control method according to claim 37further comprising the step of adjusting the respective optical phasesof the wavelength components by a wavelength phase modulator.
 39. Theoptical control method according to claim 38, wherein spatial opticalphase distributions are simultaneously controlled.